Organic Avocado Management Practice

Transcription

1 Organic Avocado Management Practice Main Points For many growers the fundamental principle that determines organic practices is managing the living part of the soil. The three aspects of soil fertility management that need attention are the soil chemical balance, ensuring a diverse range of beneficial microbes are present and feeding the soil microbial activity. Foliar sprays are used to manage stress conditions. The orchard and its surrounds are thought of as an ecosystem. As the ecosystem becomes more diverse it becomes more robust. Pest and disease management starts with managing the conditions that grow a healthy plant. Introduction The culture of avocados within an organic system has been practiced for at least 25 years in New Zealand. The longest standing organic avocado orchard was certified in There are different approaches to organic management; many of these practices have been developed by growers from their understanding of biological principles. Some of these practices have a foundation in work done by scientists or organic practitioners in other industries and some of these practices are based on the grower s experience. As such, there are few studies of the efficacy of organic production systems for avocados in New Zealand. This does not mean they don t work, but the research has not been done to establish how well they work. This chapter is intended to share the principles of organic practices. Many of the practices that are in common use are considered to have a sound basis. Sufficient progress in growing avocados organically in New Zealand has been made in recent years to give avocado growers the confidence to continue working and developing organic practices. Certification process People worldwide are becoming increasingly concerned about where their food comes from and organic certification is an established way that consumers have of discerning whether or not their food is completely free of residues and grown sustainably to an audited standard. From the grower perspective this offers recognition in the market place as well as within the grower community for the principles of how they apply their management. Certifying an avocado orchard as organic is a process that can be complex and confusing. However once systems have been established and documented it is a reasonably straight forward exercise that need not be a barrier to making the decision to certify an operation New Zealand Food Safety Authority Different regulations are in place in different export markets and some countries require government to government assurance that organic standards are appropriate for their market. The New Zealand Food Safety Authority (NZFSA) is the government body charged with administering the Official Organic Assurance Programme for New Zealand. The European Union (EU), USA and Japan all operate within this framework. The NZFSA authorises Bio-Gro and AsureQuality to certify to the standards acceptable by those markets. At the time of writing Australia is working through the introduction of a National Standard. It is expected New Zealand certifiers will be recognised as equivalent under the new system. There are some rules for the USA, EU and Japanese market that differ from other export markets. Certifiers provide the information growers need to work within these rules. Certification rules change and evolve on a regular basis, and the information in this chapter is a guide only. At the time of writing (2009) there are four options for orchards to obtain organic certification within New Zealand. PG 1 of 17

2 Avocado Growers Manual Demeter This is a certification label that is known internationally but cannot be used as an export label. It is administered by the Bio Dynamic Association and is based on the work of Rudolph Steiner. In some industries international market recognition can be gained by having dual certification with one of the full export certifiers. The Demeter label is sought after by consumers with an understanding of bio dynamic principles. There are many growers who practice bio dynamic principles without certification and often with no organic certification at all. Organic Farm NZ This is a low cost certification system intended for the New Zealand market only. It uses the Bio-Gro standard and is administered by a peer review system. Typically it is used by small orchards, allowing them to label produce as organic without needing to meet export requirements. Bio-Gro Bio-Gro is an independent body owned by the New Zealand Biological Producers and Consumers Council Incorporated and offers two levels of certification. A lower cost New Zealand market only option at a considerably reduced rate from the full export certification. Export level certification requires the certifier to implement a range of procedures that are not needed for domestic only certification. They are IFOAM accredited (International Federation of Organic Movements) as well as a Third Party Authority within the NZFSA Official Organic Assurance Programme. IFOAM was established to be an international standard recognisable across borders. Countries that are considered regulated markets do not recognise IFOAM as they have legislation that defines organic practice. AsureQuality AsureQuality offers one level of organic certification to export standard. It is a state owned enterprise that is also a Third Party Authority within the NZFSA Official Organic Assurance Programme and is IFOAM accredited. Becoming certified organic The first step towards organic certification is often to become a member of the New Zealand Organic Avocado Growers Incorporated. Membership is not required for certification but the group can assist with the information a grower needs to undertake when making decisions regarding the certification process. The information includes any sources of assistance that are available, information on current practices, seeing how growers have overcome particular issues, current marketing options and advocacy. The date of application is considered as the annual renewal date for certification. It is best to have this date before the harvest season begins as it will also become the date that the property attains full certification status once the conversion period is complete. A reduced period of conversion can be applied for based on evidence that an orchard has been practicing organics already. For export certification the application must be approved by NZFSA. Under normal circumstances the first year is considered a registration year in which the fruit has no organic status. After that it is considered conversion produce which can then be sold as organic conversion fruit alongside fully certified fruit. Depending on market conditions this fruit may achieve a similar price to fully certified fruit on the New Zealand market and at times may also be marketable as organic conversion export fruit. The first audit is always the most onerous for growers as systems have yet to be fully developed. It can take as much as a day and a half or two days to prepare for an audit which is usually two to four hours. Preparation for an audit can easily be reduced to half a day or less with experience. Primarily, working within certification is about using certified inputs. There are two levels of certified inputs: The first is approved, which means products can be used with no restriction. A copy of the invoice and the certificate current at the time of purchase is needed for the next audit. The second is restricted. These products require written approval from the certifier before use. Micro nutrients are usually in this category and certifiers ask that an explanation and possibly supporting information be given with the application for restricted use. It is preferable to have any restricted inputs detailed in the management plan that is submitted at the audit. This way any restricted inputs for the season can be approved in advance. If there is a change of plan during the year, approval can readily be asked for as needed. An audit is done by the certifier each year, looking at the records from the previous year, having a look around the orchard and approving the management plan for the next year. PG 2 of 17 October 2009 Copyright NZ Avocado Growers Association

3 increasing level of microbial complexity. This complexity tends to be reflected in the ratio of fungal activity to bacterial activity with there being more species and more overall numbers of fungi in a system that is further along the succession line. Soil within pasture is considerably more complex than the bare rock or simple soils that are dominated by bacteria. The most advanced ecosystems are old growth rain forests which support very high levels of soil life activity which are dominated by fungi. On the line of succession the avocado system is between grassland and rain forest. In practice this means that when planting and establishing trees into grass the grower needs to apply management practices that will help the soil environment support a higher level of complexity. Certified organic orchard, the sward has not been mown for several years. Establishing an Organic Avocado Orchard Site selection is important to any horticultural enterprise. For organic avocados the soil characteristics of the site will be a major factor that determines how well the orchard can be established. The drainage characteristics of the soil are particularly important as poor drainage can allow Phytophthora root rot to establish and affect the cropping potential of the trees. Trees on previously contoured sites often perform poorly when compared to trees established in undisturbed areas within the same management. Additional attention is needed to build soil quality in these areas. When establishing an avocado orchard the concept of plant succession is used. The type of plants on the land of the orchard is often changed from that of grassland to a forest environment. To successfully change, understanding the connection soil microbial succession has when establishing new plantings is required. The soil microbial complexity increases where the number of different species and the number of different kinds of species increases. For example, a soil with 10 different species of bacterial feeding nematodes is less complex than a soil with ten different species of nematode that include bacterial feeders, fungal feeders and predatory nematode species. At one end of the scale the soil is undeveloped and is primarily parent rock which supports a narrow range of lichen and bacteria. It has a low level of complexity. The plants and the soil microbes help to modify the environment preparing the ground in which increasingly complex plants and microbial life can survive. As the each new plant species establishes, the soil supports an When establishing avocado trees in pasture a major shift in the biological balance of the soil is needed. Pasture is feeding a soil microbial balance that is more bacterial than is optimum for trees. In the first few years of establishment it is important to focus management on adapting the soil environment to be more in favour of trees. Useful practices include: Up to a metre beyond the drip line of the tree should be kept clear of weeds by hand weeding for the first two seasons or until the tree is able to maintain its own vigour above the sward. If the trees are not growing strongly hand weeding may be needed for longer than two years. Companion planting to: - Promote beneficial soil microbes, e.g. oats stimulate mycorrhiza and mustard for disease suppression. - Add organic matter to the soil. Young avocado surrounded by comfrey planted as a companion plant. The grass does not get mown. PG 3 of 17

4 Avocado Growers Manual - Create habitats and provide food for beneficial - insects e.g. buckwheat and many other flowering plants. - Add nitrogen from leguminous plants, e.g. lupin, tree lucerne. - Make nutrients more biologically available. - Opening up and aerating compact soils with deep rooting species, e.g. comfrey. - Where kikuyu is a problem create a barrier using comfrey. - Provide a stock for making liquid fertiliser, e.g. comfrey. Apply mulch as a ground cover to suppress weeds and conserve moisture and promote a higher fungal to bacteria ratio this also adds soil organic matter. Grow Tree Lucerne between young trees to provide shelter in the first two years and then is mulched before they grow too large. Organic Growing Practice Many of the same practices used in conventional management can be substituted on an organic orchard as long as the inputs used are more or less equivalent to the synthetic chemicals used conventionally. For many organic growers merely substituting practices is not enough but a fundamentally different approach is needed. The biological grower considers the living part of the soil to be most important (the soil food web). In practice this means that there are three aspects to soil management: balancing the nutrient status of the soil making sure that there is as diverse a range of beneficial microbes in the soil as possible feeding the microbial activity Fertility Management Principles of Biological Soil Management The orchard and its surrounds is an ecosystem It is useful to think of the orchard and its surrounds as an ecosystem rather than the frequently held view that avocado orchards are largely monocultural systems with little bio-diversity. A wider diversity of plants will increase the diversity of microbial species, increase the habitats for a more diverse range of insect life including the beneficial insects and increase the habitats for life. As the system becomes more diverse it also becomes more robust, progressing the orchard towards a more natural environment that is more beneficial to avocado. Some growers consider a useful way to promote biodiversity is to have mixed cropping systems. This is Fungal fruiting body growing in a mixed species sward suggests a biologically active soil. clearly influenced by the business strategy the grower adopts. Another way is to cultivate as wide a diversity of non crop plants as possible in the sward and within the orchard surrounds, break up larger blocks with shelters made up of a range of species and consider trees or shrubs that may compete with cropping plants for their value in promoting these environmental benefits. Plants feed the soil Plants exude metabolites, which are soluble sugars, amino acids and other compounds pushed out by the roots into the soil. Natural systems are not wasteful, the plants are feeding the soil microbes that in turn metabolise raw materials in the soil, producing organic forms of nutrient that are favourable for the plant. Each species of plant is exuding through its roots the foods that support the types of microbes that are more compatible with that plant. In practice this means that there is yet another level of competition between the avocado and the plants around it. The tree is adapted to a soil with a higher proportion of fungi than grass plants or annuals which are not only suited to a soil dominated by bacteria but are also altering the soil to create a more bacterial environment. It is also an important aspect of the developing soil environment, maintaining microbial activity and building soil organic matter levels. PG 4 of 17 October 2009 Copyright NZ Avocado Growers Association

5 Soil health is fundamental to plant health In context of growing avocado soil health encompasses soil fertility and will include the soil structure, its moisture holding capacity as well as its level of microbial activity and the complexity of the microbial populations. How active the soil biology is and the diversity of the species has an influence on many different aspects of soil health. These include nutrient availability, organic matter processing into humus, soil crumb structure, aeration, disease suppression or disease expression, moisture holding capacity and the stability of leachable nutrients. It is a primary focus of biological growers to maximise soil biological activity and diversity. Soil organic matter and humus have a profound effect on soil properties and plant growth. Humus differs from organic matter in that organic matter includes all organic substances on or in the soil. Humus is the result of microbial breakdown of organic matter into complex stable compounds. It is not readily degraded and is relatively stable in the soil, persisting for decades. Some of the properties that humus contributes to the soil are: A high cation exchange capacity (CEC) which increases the ability of the soil to hold nutrient. Improved soil particle aggregation which improves aeration. Increased moisture holding capacity. An increase in biological activity. Sequesters carbon. Soil structure is a combination of the physical make up of the soil, the chemistry and the biological activity. How well aerated or compacted the soil is will profoundly affect the performance of the plants growing in it. Oxygen is needed by plant roots for respiration, it is also essential for microbes and generally speaking most beneficial soil microbes need aerobic (need oxygen) conditions to survive. Anaerobic (without oxygen) conditions create the conditions favourable for disease organisms including phytophthora, kill many of the beneficial microbes, allow the loss of soil nitrogen to the atmosphere and increase the leaching of nutrient. Nutrient availability is based on microbial activity in the soil rather than mineral solubility Biological systems are based on nutrient cycling driven by microbial activity. Once the trees bear a crop it requires high levels of nutrient cycling to maintain condition, grow high energy fruit and grow good quality flowering wood for the next season. Failure to produce enough high quality flowering wood is one of the reasons for orchards producing lower yields. Soil biological activity must be at a high level and the appropriate inputs are needed to support this. Within the soil there are a range of different microbes including bacteria, fungi, protozoa, nematodes and arthropods. Earthworms are larger soil organisms that also have an impact on soil health. This is referred to as the soil food web. As well as breaking down dead plant tissue they degrade chemicals and pollutants. They are also feeding on each other and this is how the plant available nutrient is generated from the raw materials. In some forms the nutrient may be chemically bound in materials that are resistant to breaking down. When the microbes are able to work on materials and release nutrients from them, these nutrients are considered as biologically available and will readily become available to the plants. Nothing works in isolation A product is usually applied or activity done with the intention of achieving a specific result. In a biological system there are complex inter relationships where that same product or activity will influence or affect a number of other aspects that indirectly affect orchard performance. For example, mowing is usually done to keep access to the orchard clear, to remove flower that bees may be visiting during pesticide applications in a conventional system and to maintain an ordered appearance. How often and when that mowing happens will also put nutrient from the trimmings back into the soil, stimulate a growth reaction that draws soil available nutrient and moisture as well as stimulating an increase in biological activity around the roots of the sward plants. The mowing may also expose the soil surface to increased drying out, remove important food sources for beneficial insects, remove flowers that would have maintained the presence of annual plants, reduce the vigour of herbaceous plants and increase the vigour of grasses. It may not be realistic or necessary to understand the full complexities of the system but it is helpful to have an awareness of and an appreciation for these complexities. Soil Management Strategies and Practices Strategies for soil biological management are: Balance the chemistry and improve fertility Standard soil tests are used to assess any soil nutrient deficiency or imbalance and the use of organically acceptable mineral fertilisers can be used to maintain the chemical balance. Many organic growers pay attention to the Albrecht theory of soil balance. Albrecht theory has been discredited by some soil scientists yet much of his work is still one PG 5 of 17

6 Avocado Growers Manual of the the bases for many practitioners including organic practitioners. It came about by testing soils where the crops were consistently yielding well. The chemical balance of these soil tests was similar. The true goal of the Albrecht model is to create the proper environment for soil biology to thrive. This depends on supplying nutrient in the proper amounts, which will determine the physical structure of the soil. When the chemical balance is right then the physical structure of the soil will be right and that will create a favourable environment for the soil biology to do well. The optimum levels of cations on the base saturation should have Calcium 68%, Magnesium 12% and Potassium 5% based on the Albrecht theory of soil balance. Biologically functional Calcium is considered to be a foundation to building soil structure as well as meeting the continuous demand for plant growth and is an essential component of microbial life. Ag lime requires a great deal of breaking down for the Calcium to become biologically available. Adding a powdered humic acid to the lime prior to spreading can help to increase the capacity of the microbes to digest the lime. Humic acid stimulates and feeds fungal activity. If it is on the surface of the lime particle that will improve the biological availability of the Calcium in the lime. Fine particle lime and microbial foods are useful tools to help maintain active Ca levels in the soil. Compost produced on farm can potentially be a high value input. If made well it can provide nutrition that has been complexed into the microbial biomass, beneficial microbial inoculum and the food sources to support soil microbial activity. Nitrogen Management Within an organic system the nitrogen taken up by the plant has largely been processed by the soil microbes from raw materials. If this is to be sufficient to meet the demands of the tree and fulfil the nitrogen supply needed to grow a crop, the right soil conditions need to be in place. There are products that supply nitrogen to the soil but these are moderated through microbial processes before plant uptake. To maintain soil nitrogen levels, manage the conditions that allow microbes that can fix atmospheric nitrogen to thrive, apply inputs that contain organic forms of nitrogen and manage the conditions to support high levels of microbial activity that will cycle nutrient in the soil: Promote clover in the sward by: - allowing the sward to grow longer - harrowing long old grass. Harrowing the grass sward maintains access and protects the soil surface. - a calcium to magnesium ratio of 7:1 and an adequate supply of phosphate, iron, molybdenum and cobalt helps to create the conditions that nitrogen fixing microbes can thrive in. There are naturally occurring free living bacteria, azotobacter, that are nitrogen fixing. - They are particularly sensitive to compacted soil conditions. Maintain aerobic conditions as below and the same soil chemical balance needed for the rhizobium in clover as above. - Inoculate with proprietary products and apply microbial foods to the soil. Apply composts, fish fertilisers and other microbe foods regularly. Build humus by applying the raw materials and maintaining the conditions that allow humus to form Addition of bulky carbon based materials into the system. Woody mulch, compost, shelter trimmings, avocado prunings and any other plant based material preferably with a woody component. Some materials can have a negative impact on the soil by slowing down microbial activity. This can result in an over wet soil and slow breakdown of the mulch. Materials such as pine, eucalyptus and cryptomeria have persistant anti fungal compounds in them. As a guide any mulch with a strong aromatic smell could cause a problem. These can still be used but before applying to the soil, any mulch that is aromatic should be aged until the smell has fully disappeared and there are signs that it has started breaking down such as visible fungal growth. PG 6 of 17 October 2009 Copyright NZ Avocado Growers Association

7 Grass if left uncut develops a wider Carbon to Nitrogen ratio feeding a more complex fibre back into the soil. It has less demand for moisture than short grass and supports a wider diversity of plants, many of which will support beneficial insect populations. There is also the benefit of reduced costs from mowing. This must be balanced against the need for access in the orchard. Harrowing can be used to flatten the sward effectively if done when growth is mature and not vigorous. Maintain the chemical balance according to the Albrecht theory. Maintain or improve soil structure Aerobic soil conditions are essential for many aspects of growing a healthy plant, it is also one of the essential conditions for healthy microbial life. Practices that help to maintain these conditions are: Increase soil biological activity and diversity. Calcium to magnesium ratio of 7:1. High levels of microbial activity. Inoculate and feed. Good levels of soil organic matter particularly humus levels. Apply bulky carbon based materials as mulch, inoculate with beneficial microbes and apply microbe foods to the soil. Maintain plant cover over the soil. Root activity penetrating the soil as well as the root exudates that help to stabilise soil aggregates and feed microbial activity are factors that help maintain aerobic conditions. Avoid vehicle traffic in the orchard, particularly during wet conditions. Increase soil biological activity and diversity Apply inputs that feed microbial populations, introduce beneficial organisms, and apply management practices that help to create favourable conditions for the biology and avoid products or practices that have negative impacts on microbes. Apply microbial products. - Compost Teas. These can deliver some of the advantages of compost at a lower cost. They can be used to enhance microbial diversity as well as lifting levels of activity. Teas are used by a number of growers, however, the results are difficult to quantify. One of the advantages of compost teas is that production is in the control of the grower and once the required machinery is in place, it is relatively cheap to produce significant volumes. - Worm extract products are similar to teas but have less active biomass. They are best used primarily as inoculum sources as well as providing some humates and other compounds that are thought to stimulate plant growth and stress resistance. As with compost teas, these can be manufactured on farm for relatively low cost. They are also available commercially. - Several commercial bio stimulants and inocula are available, usually applied at low volumes per hectare. These will be more consistent in quality than brewed products. They are often specific organisms or groups of organisms known to be beneficial to the system. There are also enzymes or stimulant products based on proprietary production processes that may stimulate activity and assist trees in times of stress. - Test for prescence of Mycorrhizae in the orchard, inoculate with proprietary products and avoid inputs that suppress them such as high levels of soluble phosphate. All orchard inputs should be applied with a mind to their effect on soil biology. This means applying products that are more compatible with the microbes, at lower rates but perhaps more often, and with a carbon source to buffer negative effects on the microbes. Applying liquid fertiliser to the ground. All fertilisers should have a carbon compound mixed with them before application. It may not always be practical; however, the purpose of having a carbon compound on the surface of the fertiliser granule is to buffer the soil microbial life from the salt effect of the fertiliser, provide a food source for the microbes to work on, so that the fertiliser is more bio available and is less leachable. Carbon sources can include: sugar, molasses, humic acid, fulvic acid and compost. PG 7 of 17

8 Avocado Growers Manual Compost The manufacture and application of compost is a valuable management tool for organic avocado growers. Compost is not a standardised product so there can be considerable variability with the results. The potential benefits of compost are increase in yield, reduced water use, improved soil properties including aeration, drainage and moisture holding capacity, reduced soil erosion and silting of waterways, better nutrient retention, improvements in disease resistance and an increase in soil carbon sequestration. Compost can also reduce weed cover and fulfil a significant part of the crop fertiliser needs. These potential benefits can be achieved because good quality, well matured compost can modify the soil environment and promote the conditions that allow humus development. Compost modifies the soil by supplying nutrients that have been metabolised by the microbes making them biologically compatible, by supplying diverse microbial inoculum and microbial foods. Composting on orchard allows control over the inputs and therefore the quality. The compost can be customized with more diversity of ingredients and by adding inoculum from commercially available products or other sources that add microbial diversity to the finished product. Fertiliser can be added into the compost to bind it into the biological biomass. Readily available material can be used and could be a part of a waste management strategy. The grower can have control over the aerobic status of the compost. If the true costs are accounted for, on orchard composting is not likely to be cheaper than commercial compost unless production is on a large scale. If attention is paid to three critical factors: recipe, aeration and moisture control, then a good quality compost can be made on the orchard. The appropriate machinery, space, raw materials, time and knowledge are all essential. Passive compost is simpler compost that can be made where the ingredients are mixed and then minimal turning is used. This should still result in a compost rich in microbial food, organic matter and with some microbial activity. For this type of compost the pile should be designed so that high temperatures that create anaerobic conditions are avoided. It would need to have lower nitrogen ingredients, coarse woodchips and the right size and shape of the windrow. An extended maturing phase of more than a year may also be needed. For organic orchards good quality compost for avocado trees is active compost dominated by fungi rather than bacteria with minimal anaerobic metabolites. The compost is stable and not still hot from the high levels of bacterial activity. There will be good levels of nutrient stored in the biomass of the microorganisms. Poorly made compost quality can be variable. Once a pile becomes anaerobic, beneficial organisms are lost and Compost pile needs to be turned every couple of days to manage temperatures during the high heat phase. potentially damaging metabolites are produced. If the pile is too dry, nitrogen is lost to the atmosphere and activity is impaired. Compost quality can be assesed by: Earthy and pleasant smell, little or no smell may indicate compost that has been effectively sterilised with minimal beneficial microbial activity. A rich medium to dark brown colour; black compost tends to have been overheated. Humus development in the compost is indicated by a very dark nearly black colour in compost that holds itself together in aggregates. There may be a sticky feel to it without it being wet to the touch. The compost is likely to have been in a maturing phase for at least six months. Fungal mycelium visibly growing through layers of the compost indicates there are likely to be good levels of basidiomycete fungi. These are a class of beneficial fungi that are particularly desirable in an orchard system. Compost should feel moist to the hand but not quite yield drops of water when squeezed. If the compost is too wet, anaerobic conditions will significantly reduce the quality. PG 8 of 17 October 2009 Copyright NZ Avocado Growers Association

9 Growth tests. Undiluted good quality compost will sprout seeds and grow them well. Purchase a fast germinating seed and sow in undiluted compost and compare sprout rates against a known control medium such as a moist paper towel. If the compost performs poorly there are likely to be inhibiting compounds present and the pile should be matured for longer or used as an ingredient for the next compost heap. Nutrient testing can be useful for nutrient budgeting but does not give any indication of microbial quality or of potentially harmful compounds. Soil Food Web testing can be used to measure biological activity. Comments on soil management practices and inputs Mycorrhizae are a group of fungi that form symbiotic relationships with plants. They form a connection with the roots of the plant and extend their hyphae out into the soil where they are more capable of picking up nutrient and water than the plant roots themselves. In return they receive sugars from the tree. They are also attributed with protecting plants from root rot diseases. Avocado specific research on mycorrhizae relationships has been minimal, however there is general Mycorrhiza inoculum available that are likely to be beneficial if the soil conditions are right. Introducing microbial inoculum of specific microbes will only achieve the intended result if the right conditions are present for the microbes to survive. This can lead to variable results which do not necessarily mean that a particular product is ineffective rather that the timing and circumstances of the application may have been wrong. Some commercial compost manufacturers can provide compost mixed with fertilisers. This may be a cost effective option but the compost has reduced value as a microbial stimulant or inoculum due to the damaging salt effect of the fertiliser on the microbes. Vermicast production on a large scale is an involved process that requires careful management to maintain quality. This is why vermicast products tend to be significantly more expensive than the equivalent volume of compost. Vermicast is considered to be much more potent than compost and is typically used at lower rates. Some growers use small scale worm systems to produce small volumes of vermicast on the orchard. This can then be used to make compost teas or vermicast extracts which can apply some of the value of the vermicast over a larger area. Worm leachate is different from extract Vermicast. It has minimal activity and is mostly the metabolites, or by products, from the worm activity such as fulvic and humic compounds. The leachate has been reported as providing beneficial growth stimulation. Proprietary inoculum, plant growth stimulants, worm extracts and compost teas must be analysed by the grower for cost effectiveness as they can at times be expensive in relation to the benefit. Any of them may be useful to develop microbial diversity and promote activity however none of them should be used as a replacement for a foundational fertility management programme which includes feeding the microbes and balancing soil nutrient. Be cautious with liquid biological products that have been manufactured anaerobically (without oxygen). Some of these have been proven to be effective; however, there may be chemicals that are the result of anaerobic processes that are phytotoxic or harmful to beneficial soil microbes. If in doubt, testing the product by applying it to young annual plants is likely to quickly show any harmful effects. There are two types of fish fertiliser commonly used: - Fish hydrolysate is the ground up remains of fish carcasses after the useable portion is removed for human consumption using specific processes to create a liquid. The fertiliser is basically liquidised fish that has been stabilised, usually by lowering the ph, so that in concentrate form it has a reasonable shelf life. It has a fishy odour but is not pungent. It is valuable as a soil microbe food and if the fish oils have not been extracted it is also a fungal food. It has a moderate nitrogen content that is largely in the form of protein. - Fermented fish fertilisers are fish carcasses that have been put through a fermentation process. The proteins and carbohydrates have been broken down and the microbes have produced metabolites, or by products. These types of fish fertiliser tend to have a pungent odour. They may have specific microbial inoculum or other raw materials such as seaweed added to them. The benefits of these products are from the inoculum of the microbes, the beneficial effect from the metabolites and the nutrient bound in the microbial biomass. Nitrogen draw down from the application of woody mulch can be an issue. When fresh material with a high carbon to nitrogen ratio is applied to the soil, the microbial population expands to consume the new PG 9 of 17

10 Avocado Growers Manual food source. Carbon is the fuel they use and nitrogen is used as a building material for their own biomass. A short term tying up of the available nitrogen can impact on plant growth. This is less likely to be an issue in a soil that has high levels of activity already and can also be lessened with the application of fish fertiliser. The particle size is also significant, as larger particles break down more slowly there is not the same bloom of bacterial growth that there is with small particles. There are a range of sources of mulch available none of which are certified as organic. To comply with organic standards a declaration from the supplier stating that the mulch has come from a source that has not been contaminated with chemicals is required. Principles of Foliar Management Microbes that inhabit the aerial parts of the tree have a significant influence on the system Just as bacteria, fungi and other microbes are ubiquitous in the soil, so they inhabit the aerial parts of the tree, the branches, leaves and fruit. The interaction between these microbes and the plant is poorly understood, but growers who have developed an appreciation for the importance of the soil microbial life also consider the interactions between microbe and plant above ground to be an important part of the biological system. Environment determines which species survive Humidity, light, temperature and food source are the main factors that determine which species of microbe are most able to grow and dominate. Predation by other microbes and insects occurs as well as competition for food sources and space. As in the soil, management practices that maximise the diversity and activity of the microbes will maximise their beneficial effects. Stress Management Flowering time, extended dry periods, pest infestation or disease are all factors that can put the tree into a state of stress. At these times the tree carbohydrate reserves will be low and this will affect its ability to respond to the conditions and maintain its health. Foliar sprays can be useful to help stimulate a response within the tree. There are products that claim to stimulate plant immune response or a growth response. There are also products that supply minerals that may be limiting the tree s ability to perform important functions, particularly sugar production through photosynthesis. One of the aims of foliar applications is to stimulate metabolic activity and particularly sugar production from increasing photosynthetic activity, within the tree until it has built sufficient reserve to maintain it s health. Foliar nutrition does not replace a soil fertility programme but depends on and works in conjunction with it. The biological perspective is that the major nutrients must be available through the soil for foliar nutrition to be effective. Foliar management strategies and practices Apply products that support the tree at times of stress Good observation of the tree performance, including leaf size, colour and density, how vigorous the growth is, any climatic events such as drought, how well the fruit is sizing and the results of insect monitoring are all important for deciding when foliar applications may be useful. Organically certified foliar nutrients are available, generally as restricted inputs, for when specific nutrient deficiencies have been diagnosed. Products that are used to support the tree at times of stress are also often effective bio foods that feed microbial life on the plant surface. Some of these are seaweed, molasses, sugar, fulvic acid, apple cider vinegar, fish fertilisers as well as proprietary products. Apply products that help to create the environment for wider microbial diversity Apply microbial products that introduce as wide a diversity of microbes as possible as discussed earlier as well as the products that feed the microbial biomass. These are seaweed, molasses, sugar, fulvic acid, apple cider vinegar and fish fertilisers. (at the time of writing, 2009, there are no certified fulvic acid products in New Zealand). Three and a half year old tree established within an organic system. PG 10 of 17 October 2009 Copyright NZ Avocado Growers Association

11 The pruning and thinning of trees is fundamentally the same as with conventional management practices. Drainage is primarily a characteristic of the soil type, it is however, influenced by the soil chemistry and the soil biology. Difficult soils can be improved by using the Albrecht principles of chemical balance as described earlier, by promoting beneficial soil microbial activity and by promoting deep rooted herbaceous or annual plants in the sward. Soil ripping or compressed air blasting can be used to physically break up compact soil structure.if used these are more likely to be successful over the long term if the biological and chemical balance is also attended to. There are also species of predatory fungi such as Beauveria bassiana, Metarhizium anisopliae, and Verticillium lecanii, that infect insects. Some of these microbes are commercially available as a spray. In the right conditions these microbes can infect and kill a range of insect species, including non target beneficial insects. Little is known about how effective it is to apply microbes like these on New Zealand avocados. Copper sprays in an organic programme One of the strategies for managing post harvest fruit rots is to promote healthy populations of beneficial microbes. These microbes are sensitive to any pesticides that are applied and likely to be killed by copper fungicide sprays. It is for this reason that although a copper spray programme of up to 3 Kg per Ha per year is allowable within organic certification, better results are more likely to be achieved with no copper sprays than with the minimal number allowable. Orchard Management Kikuyu which has not been mown for years and continues to retreat as the tree grows. The following is a list of the general points regarding orchard management, organic certification and biological principles. Contractors, such as shelter belt trimmers need to be aware of the organic status of the block before they bring machinery on site. Certifiers ask that the grower gets a statement from the contractor declaring that they have cleaned the machinery of any potentially contaminated material that could compromise the integrity of the certified property. Irrigation. One of the key benefits of a biological programme is that it builds soil organic matter including the stable humus fraction of the soil. Humus has many benefits associated with plant growth, including a significant increase in the moisture holding capacity of the soil. If the fertility programme is working well the moisture holding capacity of the soil is enhanced and the plants ability to cope with drier conditions is improved and the need for irrigation is reduced. This is difficult to quantify and the best approach is to apply considered judgment including reference to tensiometers, as to how much and how often irrigation is really needed. Points to consider when deciding on an irrigation management strategy: - Roots will grow where the conditions are favourable. The more favourable the soil conditions throughout the block, including between the tree rows, the stronger the tree roots and the more robust the trees will be. - The root zone should always be considered as significantly beyond the drip line. In an avocado orchard by the time the trees are from five to seven years old the roots are capable of colonising the entire planted area including between the rows. - Young trees have yet to develop a self sustaining root system and benefit from regular irrigation in the first two years. - Avocados rarely exhibit signs of dryness. One response is to abort fruit leading to increased summer fruit drop. Blockages in the water transporting xylem occur as a drought response. This is overcome with the growth of new wood. - Water sourced from a municipal supply should be free from chlorine. Strategies to remove chlorine include using carbon filters, allowing the water to stand sufficiently long for it to volatilise or adding humic acid. - Certifiers ask for a plan that shows the water is sourced from a contaminant free source and is PG 11 of 17

12 Avocado Growers Manual being used with within conservation principles. - Bee management. Certifiers do allow conventionally managed bee hives to be used for pollination. The grower is required to get a written confirmation from the bee keeper detailing what treatments have been used in the hives during the time that they are on certified orchards. Production Issues Weed management Principles A biological perspective on weed management means looking at weeds differently. Generally speaking a weed is considered to be any plant that is competing for resources, light, water or nutrient, with the intended cropping plant. If that same plant is also enhancing the growing environment for the cropping plant, then the definition of which plants are weeds and how to manage them is less clear. For example, plants that may be competing with the avocado may also be adding raw carbon materials to the soil helping to increase its organic matter levels and feeding soil life activity. Self established plants, such as weeds, grow best if the soil conditions suit them well. The combination of soil structure, chemistry, make-up of the soil biology as well as light and climate will influence which plants thrive. Plants that prefer conditions that are more like those that suit the avocado could be considered companion plants while those that prefer quite different conditions are also indicating that the soil balance is not optimum for the trees. In practice Weeds that are a problem in organic avocado are not so much the weed plant itself, rather the circumstances that the weed is found. Situations when weeds are an issue for avocados: Establishing young trees, generally up to three to five years old. Competition for soil moisture and the influence on the soil microbial balance from any plant that is close may have an adverse affect on growth. Once the trees have established their roots and if they maintain good vigour, they are largely able to maintain dominance over the sward growth. If trees succumb to Phytophthora the crown becomes thin as they lose leaves and any new leaf growth is small. These trees tend to have grass and annual weeds develop within the canopy area quite quickly. These plants will change the soil environment shifting it back down the succession line and exacerbate the conditions making it yet more difficult to recover the tree from the disease. Weed management in these circumstances becomes more important to help create the conditions under which sick trees can recover. Kikuyu (Pennisetum clandestinum), other creeping grasses and Wandering Willy (Tradescantia fluminescens) are particularly invasive. They are not suppressed by mulch as other grasses and annuals are and can at times appear to dominate the ground around the tree. Kikuyu thrives in a wide range of conditions and can dominate the sward particularly in warmer regions and in soils that tend to dry out. These conditions stress the competing species while the kikuyu continues to grow. It is also easily spreads in mulch. Ideas and strategies used by some organic growers to manage weeds include: Be aware of when there is a high demand from the tree for nutrient uptake and then to time input applications to support the soil life activity. Nutrient competition from weeds is considered a secondary issue to the soil influence as described in the principles of biological management. The sward plants take up nutrients and store them. As long as the biomass is not removed from the system, when the plant dies the nutrient is returned to the soil as the microbes rot down the dead plant material. There may be short term tie up of nutrient particularly during periods of vigorous growth. Increased soil life activity supports the demand for growth by breaking down dead material from the weed plants releasing the locked up nutrient. Maintain a low canopy near the ground to help shade out sward growth. This also helps to retain the leaf litter within the canopy in windy conditions. It must be balanced against not allowing large limbs to grow from low on the tree which restricts access for harvesting as the trees grow. Established trees that are growing well and supplied with an effective nutrition programme often perform well with no weed management. The damaging effect on soil life by herbicides is eliminated Companion planting with species that are considered to promote a more beneficial soil and orchard environment than grass are sometimes planted around young trees. They may also be competing with the tree for nutrient and water, but are considered to be PG 12 of 17 October 2009 Copyright NZ Avocado Growers Association

13 more beneficial overall to the system when compared to grass. These may include annuals or herbacious plants such as: - Wild flower mixes, which add diversity and food sources for insects, in a no herbicide system they can be difficult to maintain in the long term. - A plant such as lupin, which is semi woody, is a nitrogen fixer as well as a good carbon source when returned to the soil. - Oats are known to stimulate Mycorrhiza activity, chicory is deep rooted opening up aeration to deeper levels as well as returning nutrient from lower soil levels. - Comfrey is deep rooting and provides good levels of biomass which is good mulch. - Mustard is considered a bio fumigant, cleaning up diseased soils, as well as adding valuable biomass and nutrient. - Phacaelia and buckwheat are known to support predatory insects. A programme that promotes high levels of soil microbial activity applied to the kikuyu will increase the rate of breakdown of the thatch and the promote development of the topsoil. There are a number of examples where the trees will grow and fruit well despite the presence of kikuyu. Where this occurs there is a rapid rate of breakdown of the dying grass at the soil surface. The thick matting often associated with kikuyu does not occur. Observation suggests that top soil builds rapidly underneath old growth kikuyu. Wandering Willy is one of the few weeds that readily grows underneath a full avocado canopy. Crushing or cutting the Wandering Willy during dry periods will reduce this weed and add mulch to the soil helping to protect it from drying out. Observation suggests that the avocado performance may not be impaired by the presence of Wandering Willy. This weed will also add significant volumes of organic matter that breaks down. It likely competes with the tree for soil moisture. Climbing weeds such as Kapok vine (Araujia sericifera), Kiwifruit and bindweed (Calystegia sylvatica) can usually be readily managed by hand removal. Plant Health and Fruit Quality Pest and disease resistance The foundation of pest management in a biological system is maintaining good tree health. Many growers are aware that at times there are some trees that resist pest and disease problems when the neighbouring trees are affected. Organic growers from different industries commonly report that they experience reducing pest problems as their biological systems develop. There are many factors influencing whether a particular plant will be attacked or not, but there are organic and other growers who hold the view that the most important factor is the natural resistance of the healthy plant that is largely determined by the nutritional status of the tree. A holistic view is used where the grower aims to manage the conditions that allow the tree to grow to its full potential. Pest and disease management strategy utilises the different aspects of cultivating the trees in an interconnected manner. For example, if the tree is under pressure from thrips infestation, it is an indication not simply that they are present in the area but that the fertiliser programme is not sufficiently balanced to meet the demands of the tree or that there may be stress events that the tree does not have enough resources to cope with. Pest Management In addition to managing the fertility there are a number of other strategies used to manage pest issues. Broad spectrum pesticides that damage beneficial insect populations should never be used routinely and only in cases of high need. Within organic management most growers are not so concerned about maintaining pest levels as close to nil as possible, but rather allowing low level populations that are relatively stable with no population spikes and good populations of beneficial insects. Insect monitoring to establish the extent and severity of any infestation and non pest insect activity in the orchard. Building and supporting predatory insect populations is an important part of pest management strategies. Much of the time these insects go unnoticed as they are often quick moving and very small. As wide a diversity of sward species and perennial plants as possible in and around the orchard will help to support predator populations. High levels of pests may need direct intervention but must also be read as an indicator of plant nutritional problems. As such foliar nutrition should be applied whether or not pesticide products are used. Pesticides that are able to be used in a certified organic system are Bt (Bacillus thuringiensis) which is specific to caterpillars, neem oil, mineral oils and Pyrethrum, which are broader spectrum pesticides. Mineral oil and Pyrethrum will impact negatively on beneficial insect populations and should only be used at times of particular need. PG 13 of 17

14 Avocado Growers Manual A predator wasp, Thripobius semiluteus, for Greenhouse thrips. This wasp has been released on a number of organic avocado orchards in recent years. The success of the predator is difficult to assess. It is very small at about 2 mm length and therefore difficult to see in the field. Leafroller management Brown-headed leafrollers, Ctenopseustis obliquana and C. herana are the most common caterpillars causing damage to avocado crops. A third but less common species native to New Zealand, the black-lyre leafroller, Cnephasia jactatana, is also found. Light Brown Apple Moth (Epiphyas postvittana) is a leafroller that originally came from Australia and is now established in New Zealand. It is the second or third most common leafroller found on New Zealand avocados. All of these species feed on a wide range of host plants. The caterpillar damages the avocado by chewing on the leaf, what is more of a problem is the leafroller chewing on the fruit surface causing it to be rejected for export and when severe, the local market as well. The moths lay egg masses on fruit which are also quarantine issue during an export pack. Leafroller moths can lay eggs in the orchard for much of the year. Times of highest pressure are often at flowering time when the trees are under stress and during the summer. Parentia mobile. In the whole family the adults are predatory on such soft-bodied invertebrates as mites, thrips, psoccids, aphids.... The maggot-like larva is found in soil, moss, decaying vegetation, and mud, and under bark. Most larvae are predators or scavengers... Almost nothing is known of the immature stages of NZ species. The Bt pesticide is a bacteria that is only active when consumed by a caterpillar and as such it is very specific to caterpillars. Anecdotally it has been reported that the effect is improved by adding biological products to the spray. This may include bio food products such as molasses, Apple cider vinegar, a foliar seaweed product and a fish fertiliser product. Thrips management Thrips feed on the surface of the fruit sucking fruit sap causing a bronzing blemish. If this is larger than 2% of the fruit surface this fruit will be rejected for export. The adult thrips, which are black and about the same size as the pale creamy coloured juvenile thrips are capable of creating feeding damage very quickly. Foliar sprays such as mineral oil, neem oil and pyrethrum will help to reduce thrips populations. Some growers also apply seaweed, molasses and other bio foods and plant stimulants whenever thrips and Six Spotted Mite numbers become unacceptable. There are a number of certified organic products that claim to stimulate plant immune response. These may be plant elicitors, herbal tonics or fermented products. Worm extracts and seaweeds may also have a plant immune stimulus effect, but can be variable Ladybird larvae freshly hatched from egg cases on the surface of an avocado. depending on the source and production process. As discussed above the fertility programme will influence the plants ability to respond and any of these types of product are likely to be more effective if the soil programme is effectively supporting the tree. Six Spotted Mite management Six Spotted Mite infestation can be bad when the trees are drawing down on stored carbohydrate to initiate bud break, fruit set and then put out a leaf flush as well. Strategies for managing Six Spotted Mite include: PG 14 of 17 October 2009 Copyright NZ Avocado Growers Association

15 Six spotted mite feed on the leaf and in severe cases will defoliate the tree. However there are examples of orchards that have had six spotted mite present at low levels over many seasons with minimal damage. The populations will fluctuate naturally, even seeming to vanish. Adapt the fertility programme if Six Spotted Mite issues become significant. Organic pesticides such as mineral oil and neem oil will help to reduce mite populations. These are considered broad spectrum pesticides that will also affect beneficial insects and because of this should only be used once the grower has considered the benefit of applying these against the cost of the negative impact on the beneficial insect populations. Options that will not have the negative impact of the broad spectrum insecticides are products that stimulate plant pest resistance. These include seaweed products and some proprietary plant stimulant products that may be either herbal extracts or the result of specific fermentation processes. These are more likely to be effective if the tree condition is basically good and the soil fertility programme is supporting the trees effectively. Phytophthora Phytophthora cinnamomi is a root rot fungi to which avocado rootstocks are susceptible. Conventional phosphoric acid injection treatment is not acceptable within organic management. Wet compacted soils can create the conditions that favour the disease. But Phytophthora can at times become established in apparently good conditions. Biological principles suggest that low microbial activity, absence of some groups of beneficial soil microbes, particularly mycorrhizae, are also a part of conditions that favour Phytophthora. There are many orchards where the trees have never had conventional treatment and have no or only low numbers of trees that become diseased. In some blocks Phytophthora has taken hold following heavy fruit set and the trees becoming stressed as a result. It is easier to maintain trees in a healthy condition than to recover them from advanced root rot. Management options for phytophthora: If it becomes evident that Phytophthora is affecting the trees that first thing to consider is that the soil conditions have become favourable for the disease and the grower may need to apply resources that will change those soil conditions back in favour of the tree. This means treating the soil at the same time as foliar feeding the tree with growth stimulant products such as seaweed, fish fertiliser or a range of proprietary products that are designed to supply nutritional support and stimulate growth. Strategies that help to achieve this are: Certified organic avocado fruit. Soil inoculation with predatory microbes, Trichoderma and Bacillus subtilis. These are available commercially. It is prudent to inoculate with as wide a range of beneficial microbes as practical. Ensure the trees are inoculated with mycorrhizae. This is more likely to be effective as prevention than cure. Applying additional biological foods that are likely to support increased levels of beneficial microbial activity will help to shift the soil conditions to be more favourable to the plant. Treat sick trees as you would a patient in intensive care. Carry out a programme of weekly to two weekly foliar applications of nutrient and bio foods. A recipe for this is to use fish fertiliser, seaweed, molasses and a foliar calcium spray. Any foliar calcium spray would need to be a certified product and may require restricted permission. Additional mineral fertilisers beyond what is recommended for the fertility plan in general should not be applied to sick trees. It is the microbial balance that needs to be changed and any application beyond a known need for balancing the soil chemistry may negatively impact on the soil biology. Thin or remove fruit. A more practical option on larger trees is severe flower thinning. Sick trees will often set a large crop yet the fruit fails to size well and is usually badly affected by sun burn. The fruit also diverts much of the sugars that the tree produces away from supporting root and leaf growth. PG 15 of 17